Simulation of Dimensional Changes and Hot Tears During Solidification of Steel Castings: Final Technical Report

Christoph Beckermann; Kent Carlson

During solidification, contractions or distortions of the steel, known as “dimensional changes,” can cause the final product to vary significantly from the original pattern. Cracks in the casting that form during the late stages of solidification, called “hot tears,” occur when contractions can no longer be accommodated by residual liquid metal flow or solid metal displacement. Dimensional changes and hot tears are major problems in the steel casting industry. These occurrences are difficult to anticipate and correct using traditional foundry engineering methods. While dimensional changes are accommodated using pattern allowances, the desired dimensions are often inaccurate. Castings that form hot tears must then be scrapped or weld repaired, expending unnecessary energy. Correcting either of these problems requires a tedious trial-anderror process that may not necessarily yield accurate results. A model that predicts hot tears and dimensional changes during steel casting solidification has been successfully developed and implemented in commercial casting and stress analysis software. This model is based on a visco-plastic constitutive model with damage, where the damage begins to form when liquid feed metal is cut off to a solidifying region. The hot tear prediction is a locater for hot tear initiation sites, and not a full tear prediction: casting regions with relatively high damage values indicate where a casting is more likely to tear. In addition to model development, experimental castings were designed and produced, to provide both hot tear and dimensional change data during casting solidification and cooling. In both experimental castings and industrial production castings, regions of high damage were seen to correlate reasonably well with hot tear locations. Reasonable prediction of dimensional changes was also seen. The predictive capability of the model will improve with the development of more accurate high-temperature mechanical properties. The hot tear/dimensional change model provides the steel casting industry with a tool that will result in a reduction of scrapped castings and re-work/repair due to dimensional changes or hot tears, and also an increase in casting yield due to a reduction in the use of padding and improved placement of risers, leading to better riser efficiency. This new technology is expected to result in an estimated energy savings of 2.15 trillion BTU’s/year. Along with these energy savings, reduction of scrap and improvement in casting yield will result in a reduction of the environmental emissions associated with the melting and pouring of the metal which will be saved as a result of this technology.

Simulation of Dimensional Changes and Hot Tears During Solidification of Steel Castings: Final Technical Report

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